Thankfully someone else is having the same issue as me (from what you're describing.) I'm assuming those black boxes were put in by you to protect your privacy correct?

Try my temp solution by disabling HW acceleration described here and see if it fixes it (at least temporarily until we can get some official "addressment" of the issue): https://support.mozilla.org/en-US/questions/1067959#answer-743232

No, the black boxes were not put by me. that is how the screen is rendering

ok, turning off hardware acceleration seems to be helping. if the problem comes back will repost.

I have the same problem. Posted it on July 22 and just noticed this thread. When I move the mouse over the areas that are black, they come in. Trying the fix. Win 8.1 is a piece of crap. Re loaded Mozilla and changed the setting with the hard ware acc. and it still is a problem.

All of win 8 is a piece of crap. I expect nothing better from Win 10. Bring back XP. It is like going from George H to George W.

Btw, my issues stopped a month ago after updating to "31.1.0", released on 9 July. Hw acceleration turned back on and everything is fine. Initially I thought it was an OC issue with my gpu but after further testing that wasn't the case.

I have the same problem. On latest version of Thunderbird (38.2.0) but it still happens. A mixture of black panels and notrmal screen, that only clear when the cursor runs over them. Most annoying.

I switched to Sea Monkey, solved that problem. Only thing I don't like is when you open a link, it uses the sea monkey browser instead of your default browser. I could not find any settings to change that. If anyone knows......PLEASE post.